Method of gilding sheets, notably for making stamps

ABSTRACT

This method of manufacturing metal coated sheets, mainly goldcoated or gilded sheets, for making postage stamps, comprising depositing by the serigraphic process, on an absorbent sheet, a homogeneous composition of fine metal powder, binder and solvent, in several successive layers, with a drying step between successive applications, and fixing and polishing said layers by repeatedly passing the sheet through a polishing machine comprising a cylinder coated with very hard rubber and a cylinder of hardened steel, these cylinders being urged against each other by a pressure of the order of 300 to 500 psi.

United States Patent 1 Bletry et al.

[451 Oct. 21, 1975 METHOD OF GILDING SHEETS, NOTABLY FOR MAKING STAMPS [75] Inventors: Pierre C. Bletry; Bernard E. David,

both of Paris, France [73] Assignee: Pierre Mariotte S.A., Paris, France [22] Filed: July 2, 1973 [21] Appl. No: 375,864

[30] Foreign Application Priority Data July 5, 1972 France 72.24295 [52] US. Cl. 427/272; 101/129; 427/360 [51] Int. Cl B44d 1/52 [58] Field of Search 117/13, 15, 27, 28, 31,

[56] References Cited UNITED STATES PATENTS 3,085,025 4/1963 Eaton 117/33 X FOREIGN PATENTS OR APPLICATIONS 1,444,308 5/1969 Germany 117/64 R Primary ExaminerRalph S. Kendall Assistant ExaminerBruce 1-1. Hess [57] ABSTRACT This method of manufacturing metal coated sheets, mainly gold-coated or gilded sheets, for making postage stamps, comprising depositing by the serigraphic process, on an absorbent sheet, a homogeneous composition of fine metal powder, binder and solvent, in several successive layers, with a drying step between successive applications, and fixing and polishing said layers by repeatedly passing the sheet through a polishing machine comprising a cylinder coated with very hard rubber and a cylinder of hardened steel, these cylinders being urged against each other by a pressure of the order of 300 to 500 psi.

1 Claim, No Drawings METHOD OF GILDING SHEETS, NOTABLY FOR MAKING STAMPS BACKGROUND OF THE INVENTION.

The present invention is concerned with improvements in the methods of producing by the silk-screen process sheets coated with precious metal such as gold, notably for manufacturing postage stamps and the like.

The manufacture of postage stamps on golden sheets was accomplished heretofore from gold leaves rolled to variable thickness, of the order of a few thousandths of millimeter, or hammered gold leaves having a thickness of from 1 micron to 2 or 3 scores of microns. Stamps are also manufactured from golden sheets by using gold films deposited on a generally cellulose support, the thickness of these films being however of the order of a few Angstroms, but the quantity of gold contained in stamps of this character is extremely small, so that the process may be regarded more as the metal coating or metallization of a paper sheet constituting the stamp proper than forming a stamp on a golden sheet.

In the case of postage stamps manufactured from rolled or hammered golden leaves, serious difficulties are frequently encountered on account of the irregularity or unevenness, even if very small, observed on the golden leaves emerging from the rolling or hammering operation. Now, one of the basic requirements of Countries issuing postage stamps, irrespective of the nature of the support (paper, metal or else) lies in the absolute identity of all the stamps constituting a same issue. This identity applies of course not only to the constancy of the printing quality, to the absence of var- SUMMARY OF THE INVENTION It is a primary object of this invention to improve the method of depositing precious metal on a support in order to obtain a perfectly regular, homogeneous and constant metal coating thereon.

It is another object of this invention to provide an im- 'proved method of manufacturing postage stamps printed on golden sheets which remain definitely identical to themselves throughout the issue and are free of any defects or variations, so as to positively eliminate any possibility of issuing a faulty stamp.

The idea that comes immediately to ones mind for meeting these requirements is to further improve the physical division of the metal, beyond the sheet or leave of hammered gold, i.e. producing a powder of such fineness that the end product can be regarded as a perfectly homogeneous one.

Various methods have already been used to this end, such as the preliminary coating of the paper sheet with an adhesive substance (shellac, for instance, and cements of various origins), before spreading the metal powder (bronze, aluminium, copper, etc. in excess quantity. In the case of current metal powders the excess powder is recovered more or less, but obviously such approximation could not be accepted when using noble or precious metal powders such as silver or gold.

on the other hand, since an excess amount of metal powder is spread onto the paper surface, a well-known powdering effect takes place, i.e. not all the powder particles are retained by the adhesive substance so that part of these particles sticks to the operators fingers and also to the fingers of anybody subsequently handling or simply touching the powder-coated sheet. Finally, the adjustment of the rate of application of the metal powder to the sheet is not sufficiently accurate to positively warrant a constant weight per surface unit of powder adhering to the sheet.

Another known method consists in fixing the metal powder to its support by means of the serigraphic or silk-screen process. This process consists essentially in mixing the metal powder with a binder and a solvent, and subsequently apply the mix to the sheet through a silk (and mostly Nylon) screen or wire gauze stretched in a rigid frame. Thus, metal powder deposits formed either on flat-tint surfaces or on decorative patterns reproduced as resists on the silk-screen are obtained. Although this process is advantageous on account of its relative regularity, it is still objectionable on account of the powdering effect and therefore of the removal, by rubbing, of a certain amount of powder after the application. Moreover, the surfaces thus obtained are relatively dull.

It is the essential object of this invention to produce golden sheets by applying the serigraphic process, the sheets thus obtained being characterized in that:

a. they are free of the above-mentioned powdering effect;

b. their weight of gold per surface unit is constant;

0. they preserve the brightness of gold even after the application of the gold-containing printing paste.

Moreover, since stamps made from golden sheets are intended to be embossed for setting in relief certain areas of the vignette (effigies or facial values, for instance), it is an essential requirement that the various treatments to be applied to the golden sheets shall not produce any distortion thereof, for such distortion would definitely prevent the necessary coincidence or matching of the subjects deposited on the golden sheet through a serigraphic process or another process with the subjects or patterns engraved on the tool means used for the embossing operation.

All these requirements lead to the successive implementation of the following operations, in the specific case of golden sheets for making postage stamps.

On a suitable support, such as an adhesive-coated offset paper, which must have an absorption capacity sufficient to take at least one fraction of the binder coating the particles of gold powder, there is deposited through a serigraphic screen a printing paste consisting of a mixture of gold powder with a cellulose binder and a solvent. These ingredients must be metered with a great care in order to maintain the weight of deposited gold to a constant value.

However, this serigraphic process for transferring gold to certain sheet areas corresponding to the relief design would not be sufficient for properly controlling the regularity of the gold deposit.

DESCRIPTION OF THE PREFERRED EMBODIMENT According to the present invention, the printing takes place in several passes with a drying step between two successive passes, to permit a proper control of the weight of deposited gold particles. These successive passes are necessary for eliminating the abovementioned powdering effect, each successive layer causing the underlying layer to be safely fixed on the sheet surface.

To improve the fixation and at the same time recover the metal brightness, and according to a specific feature of this invention, the golden sheet thus obtained is introduced into a polishing machine specially designed for this purpose. Thus, the golden sheet is passed between a very hard rubber cylinder and a carefully ground and polished hardened steel cylinder, both cylinders being urged against each other by using a constant hydraulic, pneumatic or mechanical pressure, so that the sheet eventually emerging from this machine is extremely glossy while having all the desired properties, without having undergone any distortion.

The metal brightness is further improved by repeating this polishing operation.

EXAMPLE For manufacturing a golden sheet intended for making postage stamps, there are used a printing paste consisting of a mixture of fine gold powder and a binder, dissolved in a cellulose solvent, and a serigraphic screen on which the resists corresponding to the ornamental designs or patterns of the stamps are reproduced. The screen receives several layers, and a drying step is reserved between successive applications, so that each deposit or coating of said composition on the support or carrier sheet disposed and adjusted under the screen is fixed by the next deposit or coating. To this end, a machine comprising positioning members on the serigraphic screen and means for depositing the composition, scraping off the excess as well as means for evaporating the solvent between successive applications, are provided.

Yet, the sheet emerging from this machine, which is coated with several regular and homogeneous layers of gold on a thickness of a few microns, has a full appearance and the last layer, even when dry, displays the above-mentioned powdering effect. To eliminate this inconvenience, the sheet is subsequently introduced one or preferably several times into a smoothing or polishing machine comprising a cylinder'lined with very hard rubber and a hardened steel cylinder, these two cylinders being urged towards each other under a strictly constant but adjustable pressure of the order of 300 to 500 psi. The sheet issuing from this machine meets all the above-defined requirements and can be subsequently subjected to the known embossing, pigmenting, printing and perforation operations.

Of course, it will readily occur to those conversant with the art that this invention should not be construed as being strictly limited to the manufacture of postage stamps, since it is also applicable to various other fields in which metal powder, notably silver, copper and bronze, are used. Besides, the resists formed on the serigraphic screen are subordinate to the ornamental or functional pattern contemplated.

What is claimed is:

l. A method of manufacturing sheets of stamps comprising relief areas coated with gold powder which alternate with resist-printed areas, comprising depositing through a previously prepared serigraphic textile screen a mixture of very finely divided gold powder with a binder and a solvent on an offset paper sheet having a glue coated back, repeating this step according to the desired thickness of the gilded areas while allowing the coat to dry between at least two successive passes until a homogeneous metal layer adhering perfectly to the sheet areas to be gilded has been obtained, color-printing the other resist areas of the stamp and imparting the desired luster to the gilded areas by a calendering performed between a rubber-coated cylinder and a carefully ground and polished hardened steel cylinder, said cylinders being urged against each other by an adjustable and constant pressure. 

1. A METHOD OF MANUFACTURING SHEETS OF STAMPS COMPRISING RELIEF AREAS COATED WITH GOLD POWDER WHICH ALTERNATE WITH RESIST-PRINTED AREAS, COMPRISING DEPOSITING THROUGH A PREVIOUSLY PREPARED SERIGRAPHIC TEXTILE SCREEN A MIXTURE OF VERY FINELY DIVIDED GOLD POWDER WITH A BINDER AND A SOLVENT ON AN OFFSET PAPER SHEET HAVING A FLUE COATED BACK, REPEATING THIS STEP ACCORDING TO THE DESIRED THICKNESS OF THE GILDED AREAS WHILE ALLOWING THE COAT TO DRY BETWEEN AT LEAST TWO SUCCESSIVE PASSES UNTIL A HOMOGENEOUS METAL LAYER ADHERING PERFECTLY TO THE SHEET AREAS TO BE GILDED HAS BEEN OBTAINED, COLOR-PRINTING THE OTHER RESIST AREAS OF THE STAMP AND IMPARTING THE DESIRED LUSTER TO THE GILDED AREAS BY A CALENDERING PERFORMED BETWEEN A RUBBER-CYLINDER AND A CAREFULLY GROUND AND POLISHED HARDENED STEEL CYLINDER, SAID CYLINDERS BEING URGED AGAINST EACH OTHER BY AN ADJUSTABLE AND CONSTANT PRESSURE. 